linux - sem_init on ubuntu using C-Language -


i working on code uses pthread , semaphore libraries. here code dose not work , think because of sem_init function. new in c , don't know how use sem_init, sem_open, sem_wait , sem_post. can give me advice??

#include <sys/mman.h> #include <math.h> #include <wait.h> #include <stdio.h> #include <stdlib.h> #include <semaphore.h> #include <sys/sem.h> #include <sys/types.h> #include <unistd.h> #include<fcntl.h> sem_t sem1,sem2;  float calculate(int a,int b) {     float d = ((a *a) + (b*b))/2;     return d; }  int main() {     int q;     int i,j,x;     float *maddress, m, sum;      maddress=mmap(null,sizeof(float),prot_read|prot_write,map_shared,-1,0);      sem_init(&sem2,0,1);     sem_init(&sem1,0,0);     sem_open("sem2",o_creat);     sem_open("sem1",o_creat);       if((q = sem_init(&sem1,1,0))!=0)         printf("error in create\n");      for(i=1;i<=10;i++)     {         j=fork();         if(j==0)         {              printf("the child %d executing\n",i);             m=calculate(i-1,i);             printf("child %d calculated value: %f\n",i,m);             sem_wait(&sem2);             maddress=&m;             sem_post(&sem1);             exit(exit_success);         }     }                for(j=1;j<=10;j++)     {         wait(&x);         if(wifexited(x))         {             sem_wait(&sem1);             sum=sum+ (*maddress);             sem_post(&sem2);           }     }     printf("the final result is: %f \n",sum);      sem_close(&sem1);     sem_close(&sem2);     return 0; }

(1) there 2 kinds of posix semaphores - named , unnamed - , mixing both. unnamed semaphores use sem_init , sem_destroy. named use sem_open,sem_close , sem_unlink.

(2) assuming want unnamed semaphores, fine related (i.e. forked) processes doing, must put semaphores shared memory before start forking. putting semaphore process memory won't shared between children , parent because every child own copy of memory , therefore, in effect, own set of semaphore not related other process.

your program hang forever in parent @ sem_wait(&sem1) because children signaling entirely different copy of sem1.


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